中文摘要：

为了解若尔盖高原高寒草地沙化过程生态系统中CO2的收支变化,利用Li-840静态箱法于2013年生长季（5-10月）,在一处典型沙化区域,分别调查未沙化（UN）、中度沙化（MO）和重度沙化（SE）草地的生态系统净通量（NEE）、生态系统呼吸（ER）和土壤呼吸（SR）的季节和日动态变化.结果显示：若尔盖高寒草地未沙化草地和中度沙化草地NEE季节变化呈单峰状,中度沙化草地波动性增强,而重度沙化草地在整个生长季节变化不明显.未沙化草地在生长季节日间瞬时NEE为-3.33μmol m^-2 s-1,中度沙化草地为-2.06μmol m^-2 s^-1,是未沙化草地的61.86%,严重沙化草地为-0.62μmol m^-2 s-1,是未沙化草地的18.61%.在沙化过程中,土壤所贡献给生态系统整体的呼吸占比,从72.90%增加到79.28%,季节变化动态呈现出与系统呼吸相似的变化规律.未沙化草地在生长季节的初期和中期均呈现出较强的碳汇特性,固碳速率分别为9.05 g m^-2 d^-1和28.70 g m^-2 d^-1,而在末期呈现出微弱碳源.本研究表明,沙化使得高寒草地在生长季节由微弱的碳汇转变成为碳源,固碳能力严重削弱.

英文摘要：

To detect the changes of carbon dioxide budget during the desertification process in alpine grasslands ecosystem,we investigated in a typical desertification area on the Zoige Plateau the net ecosystem carbon fluxes（NEE）,ecosystem respiration（ER） and soil respiration（SR） in undesertified（UN）,moderately desertified（MO） and severely desertified（SE） grasslands with the Li-840 static box system in the growing season（May to October）.Our result showed a unimodal curve in seasonal NEE of the UN grassland and MO grassland;the dynamics of seasonal NEE was significantly enhanced in the MO but had no significant change in the SE.The average of NEE during the growing season was-3.33 μmol m^-2 s^-1 in the UN,-2.06 μmol m^-2 s^-1 in the MO（61.86%that in UN）,and-0.62 μmol m^-2 s^-1 in the SE（18.61%that of UN）.During the process of desertification,the proportion of SR in ER increased from 72.90%to 79.28%,with the seasonal variation of SR similar to that of ER.UN in the early and mid growing season was a carbon sink with a carbon sequestration rate of 9.05 g m^-2 d^-1 and 28.78 g m^-2 d^-1 respectively;but it became a weak carbon source in the end of growing season.Our research indicated that desertification may change alpine grassland from weak carbon sink to carbon source in growing season,greatly weakening its carbon sequestration capacity.